1. Field of the Invention
The present invention relates to a gas sensor processing apparatus for processing the output of a gas sensor which detects the concentration of a specific gas.
2. Description of the Related Art
Conventionally, a gas sensor has been used which is disposed in an exhaust pipe of an internal combustion engine of a vehicle and is adapted to detect the concentration of a specific gas contained in exhaust gas for the purpose of, for example, controlling the air-fuel ratio of fuel mixture supplied to the internal combustion engine. For example, an oxygen sensor for detecting the concentration of oxygen and an NOx sensor for detecting the concentration of nitrogen oxide (NOx) are known. In these gas sensors, a solid electrolyte body mainly made of zirconia (zirconium oxide) is commonly used as a detection element. The solid electrolyte body exhibits good oxygen ion conductivity at a high temperature of about 600° C. or higher (activated state). Also, by utilizing a phenomenon that the impedance (internal resistance) of the detection element changes with the element temperature, the temperature of the detection element is detected. Further, in order to maintain the detection element at a predetermined temperature within a range in which the detection element becomes active, the supply of electric current to a separately provided heater is feedback-controlled such that the element impedance becomes equal to a target impedance.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No H10-26599